1. Field of the Invention
The present invention relates of a method for stabilizing a flame retarded polyurethane foam against scorching and the product thereof.
U.S. Pat. No. 3,798,184 has suggested that polyurethane foams can be stabilized against scorching caused by dry heat degradation by the incorporation therein of an effective amount for stabilization of a diphenylamineacetone reaction product. That patent indicated that N,N'-di-sec-butyl-p-phenylenediamine, a known antioxidant for natural and synthetic elastomers (e.g., see U.S. Pat. No. 3,138,571, Belgium Pat. No. 778,579 and U.S. Pat. No. 3,157,615), when incorporated by itself in a polyurethane foam, failed to protect the foam from dry heat degradation. Polyurethane foam formulations have contained a variety of phenylenediamines in combination with other functional additives (e.g., see British Pat. No. 873,697 and U.S. Pat. No. 3,194,793), but it has not been realized that the N-alkanoyl-N,N'-dialkyl-phenylenediamine compounds intended for use in the present invention will, unlike N,N'-di-sec-butyl-p-phenylenediamine, prevent scorching in a flame retarded polyurethane foam. Moreover, these substituted N,N'-dialkyl phenylenediamines also improve the indentation load deflection, as measured by ASTM D1564, Method A, of such foams.
The N-alkanoyl-N,N'dialkyl phenylenediamine compounds intended for use herein have the formula: EQU (H)(R)NC.sub.6 H.sub.4 N(R)(COOR.sup.1)
wherein R and R.sup.1 can be the same or different and are straight chain or branched alkyl, e.g., C.sub.1 -C.sub.10 alkyl. The nitrogen atoms are preferably para- on the benzene ring although ortho- and meta- isomers can also be utilized. A preferred compound is N-heptanoyl-N,N'-di-sec-butyl-paraphenylenediamine.
The substituted phenylenediamine compounds intended for use herein are preferably formed by acylating an N,N'-dialkyl phenylenediamine reagent with the appropriate alkanoic acid under any of the well known acylation conditions. The reaction can be carried out at an elevated temperature, normally in the range of from about 100.degree. to 300.degree. C. Alternatively, the phenylenediamine reagent can be reacted with the acid anhydride of the appropriate acid at a temperature of about 20.degree.-200.degree. C. The third method involves reacting the phenylenediamine reagent with the selected alkanoyl chloride at a temperature of about 20.degree.-150.degree. C. If either the second or third route is used, an acid acceptor such as a tertiary amine can be employed to improve the yield and prevent side reactions. Pyridine appears to be particularly suitable although any art recognized acid acceptors can be used. Such processes are described in British Pat. No. 1,326,875.
The alkanoyl-N,N'-dialkyl-phenylenediamine compound can be incorporated either alone or in admixture with one another in any of the foam formulations of the type described, for example, in U.S. Pat. No. 4,143,219, which is incorporated herein by reference, in order to stabilize the polyurethane foam against scorching. The amount of such compound which is used can range from about 0.01% to about 5% by weight of the foam formulation, preferably from about 0.2% to about 3% by weight, of the formulation. Such foam formulations are prepared by mixing an organic isocyanate with a polyol compound which is, preferably, a polyol having a molecular weight in the range of from about 3000 to about 5600. Particularly preferred polyurethane foam formulations are those flexible and low density foams which contain such organophosphorus flame retardants as the homopolymerization product of tris (2-chloroethyl) phosphate, the copolycondensation product of bis (2-chloroethyl) vinylphosphate and dimethyl methylphosphonate, the copolycondensation product of tris (2-chloroethyl) phosphate and dimethyl methylphosphonate. Such products are described in U.S. Pat. Nos. 3,513,644, 3,641,202, 3,695,925, 3,822,327 and 3,855,359.